Sailboats
A sailboat is a vehicle which travels on water, propelled by wind.
Kite Propulsion
A kite is an airfoil assembly tethered to the ground, to a person, or to something not moving with the wind. Kites are used to propel some sailboats. U.S. Pat. No. 57,996 to Chester W. Sykes is of a broad, flat balloon supporting sails for a sailboat. If used, the balloon would act as a kite. U.S. Pat. No. 4,497,272 to Sidney E. Veazey, U.S. Pat. No. 5,213,289 to David P. Barresi, U.S. Pat. No. 5,366,182 to William G. Roeseler and Cory Roeseler, and U.S. Pat. No. 5,435,259 to Gaudencio A. Labrador are of propulsion by kite. A kite produces a controllable force applied at a convenient point on a sailboat and operates in faster, smoother air than any other sailing device. Disadvantages of kites include difficulty in launching, possible tether entanglements with other objectsxe2x80x94therefore requiring large air space, and a lower lift-to-drag ratio than other means due to the use of cloth and wind drag on tethers.
Multi-Hull Boats
A catamaran is a boat with two parallel hulls arranged so that it has more stability than said two hulls when separate. A trimaran is a boat with three hulls. Other multi-hull configurations have been proposed or tried. In general, a multi-hull boat is much more stable than a single hull of equal displacement. The exception to this is a multi-hull boat entirely capsized, in which case it is generally very stable in its capsized orientation, resisting return to an upright orientation.
Balancing Forces
A sailboat is acted on by forces: gravity, aerodynamic forces (from wind), buoyant forces and hydrodynamic forces (from motion of water relative to boat). The aerodynamic forces act on parts of the boat above water. The hydrodynamic forces act on parts of the boat underwater and oppose aerodynamic forces. This creates an undesirable moment causing the sailboat to lean.
A good solution is to cause all forces to act on one point, eliminating the moment. Kite tethers manifest the tension force, which is normally made to act on a boat""s center of hydrodynamic lateral resistance. U.S. Pat. Nos. 612,209 to Fredrik Ljungstrxc3x6m, No. 1,670,936 to Malcom McIntyre and Thomas A. McIntyre, No. 1,885,247 to John Phillips Fox, No. 2,126,665 to John T. Rowland, No. 2,170,914 to Rudow Rummler, No. 2,329,220 to Rudow Rummler, No. 3,094,961 to Bernard Smith, No. 3,455,261 to Hugh Perrin, No. 3,631,828 to Bernard Smith, No. 3,981,258 to Bernard Smith, No. 4,228,750 to Bernard Smith, No. 4,458,859 to Aaton P. Ganev, No. 4,478,164 to Michael J. Menear, No. 4,671,198 to Edwin des Snead, No. 4,708,075 to Edwin des Snead, No. 4,852,507 to Randall C. Ryon and Robert A. Austin, No. 4,864,949 to Eric Olsen, No. 4,934,296 to Bernard Smith, and No. 4,945,845 to James L. Johnson are of sails intended to align aerodynamic sail force with the boat""s center of lateral resistance.
Airfoils and Hydrofoils
A hydrofoil is a wing intended for use under water. Often, sailboat keels and rudders are hydrofoils. Also, hydrofoils have been fitted to sailboats so as to lift the hull free from the water at high speed. The following are examples of such sailboats: John G. Baker""s Monitor, Donald J. Nigg""s Flying Fish, David A. Keiper""s Williwaw and Greg Ketterman""s Trifoiler.
A hydrofoil commonly has a sharp trailing edge and convex curved upper surface. Such shapes are the most efficient if attached water flow over the entire foil can be maintained. But for hydrofoils operating near the water surface, which is the case for all high-speed sailboats, two phenomena tend to occur which prevent such desired attached flow and reduce efficiency: ventilation and cavitation. Ventilation is the entrance of air into the flow of water around the foil and occurs with surface-piercing foils. Small planar surfaces attached perpendicularly to the hydrofoil, called fences, can eliminate some ventilation. Cavitation is the formation of water vapor bubbles in low-pressure areas of the flow. Near the water surface and in the absence of ventilation, cavitation is inevitable at speeds above a threshold of around 60 knots. Hydrofoils shaped to be efficient at speeds below this threshold are called subcavitating; those shaped to be efficient at speeds above this threshold are called supercavitating. Supercavitating hydrofoils may have a blunt trailing edge and a sharp leading edge and are generally less efficient than subcavitating foils at low speeds. But they are more efficient than subcavitating foils at high speeds. Recently much effort has been made to avoid cavitation, but supercavitating foils are the best available solution for speeds beyond the threshold.
A wingsail is an airfoil used for a sail. It can have a higher lift/drag ratio than a sail and therefore is more efficient than a sail when the relative wind is at a small angle to the course of the sailboat, for example, when close-hauled or tacking.
Aerohydrofoils
Bernard Smith defines the word aerohydrofoil on page 3 of his book, xe2x80x9cThe 40-Knot Sailboatxe2x80x9d, 1963:
xe2x80x9cStated in the simplest possible terms, the machine for deriving the ultimate in sailing speed consists of two vertical wings, an inverted one in the water joined to an erect one in the air. When coupled in this way the assembly may be likened to a sailboat that has a sail and a centerboard, but no hull; except that the sail is no longer a sail but an airfoil, and the centerboard is no longer a centerboard but a hydrofoil. In fact it is no longer a traditional sailboat and therefore has been renamed an xe2x80x98aerohydrofoil.xe2x80x9dxe2x80x99
I use aerohydrofoil to mean xe2x80x9ca wind-propelled water vessel (sailboat) that consists mainly of airfoils and hydrofoilsxe2x80x9d.
U.S. Pat. Nos. D337300 to Ernst-August Bielefeldt, No. D345542 to Ian J. Duncan, No. 2804038 to Hugh M. Barkla, No. 3,425,383, No. 3,532,067, No. 3,646,902, No. 5,063,869 to Ernst-August Bielefeldt, No. 5,113,775 to Robert W. Imhoff, No. 5,136,961 to Harold E. Follet, are of aerohydrofoils. Several model sailboats built by Bernard Smith and the full-size sailboats Yellow Pages Endeavour, by Lindsay Cunningham, and the French Vecteur Vitesse are successful aerohydrofoils. Aerohydrofoils are fast and efficient. Generally, they are complex and have limitations, such as linited performance on one tack, or confinement to smooth water.
Aerodynamic Control
High speed travel over water requires stability. If that stability come from the water, the sailboat must continuously have a control element in the water. A better solution is to derive stability and control from the passing air because the sailboat is always surrounded by air. The theoretical Merrimac described by Bernard Smith in xe2x80x9cThe 40-knot Sailboatxe2x80x9d utilizes air rudders. John G. Walker has built successful wingsail sailboats with aerodynamic control of the wingsail (see U.S. Pat. No. D324,021). Robert W. Imhoff has built boats basically per his U.S. Pat. No. 5,113,775 in which, through a combination of sail and keel settings, the wind automatically correctly orients the boat.
Airborne Sailboats
A further improvement is to combine aerodynamic stability with airborne flight. Some sailboats travel fast enough to leave the water for limited distances. This is often an uncontrolled, nearly ballistic, mode of travel. Kite-propelled waterskiers and sailboard sailors have intentionally and somewhat controllably become airborne. U.S. Pat. No. 3,800,724 to Richard R. Tracy, No. 3,899,146 to James L. Amick, No. 3,966,143 to Gordon R. Smith, No. 3,987,982 to James L. Amick, No. 4,450,784 to Ellis Mellinger, No. 4.458,859 to Aaton P. Ganev and No. 5,181,674 to William J. Apgar are of sailboats which could become airborne.
The sailing machines defined in Amick""s U.S. Pat. No. 3,899,146 and No. 3,987,982 and the self-launching glider described in Smith""s U.S. Pat. No. 3,966,143 have the following disadvantages. The entire craft to flips to change tack. The cockpit is always tilted, except when changing tacks. The maximum wind force available is limited by the weight of the craft; that is, if an aerodynamic force beyond some threshold is applied, the craft necessarily becomes airborne, willy-nilly.
The hand-carryable flying sailboat described in Mellinger""s U.S. Pat. No. 4,450,784 lacks aerodynamic control of relative wind direction.
The vehicles described in Tracy""s U.S. Pat. No. 3,800,724 and Apgar""s U.S. Pat. No. 5,181,674 require major changes in wing setting to change tack.
Land Yachts and Ice-Boats
Sailing craft exist for travel on land and ice (called, respectively, land yachts and ice-boats). In such craft, wheels or runners correspond to the hulls and hydrofoils of sailboats. Because of the availability of large flat surfaces of dirt or ice and because, generally, wheels and runners are lighter and efficient over a wider range of speeds than hulls and subcavitating hydrofoils, land yachts and ice-boats have achieved higher speeds than sailboats. But the problem of stable airborne behavior has not been solved in practice. So all such high-speed craft are designed to stay attached to the surface by ballast or aerodynamic force.
Aircraft
Fixed wing aircraft, and gliders in particular, of high efficiency have been developed. But no such actual aircraft have been launched by wind power alone. Therefore, all aircraft presently rely on other sources of power.
At present, the world sailboat speed record is under 50 knots, there is no aerohydrofoil suitable for transportation and there is no successful wind-launched sailplane. That is the state of the art.
The object of the present invention is high speed wind propelled travel. Advantages of the present invention include superior maneuverability and control, stability in high winds, and stability in foilborne operation over moderate waves. Another advantage is the use of efficient supercavitating hydrofoils to eliminate any cavitation or ventilation problems. Compared to some boats of the prior art, this invention is simpler. Thus construction is easier and lighter. This invention can make a smooth transition from foilborne mode to airborne mode. No weight shifting or extreme changes in pilot position or attitude are required for any mode or change in mode of operation.